Rear end and big tires

[Mertz]

I have my 72 C20 running as good as possible. Timing, Qjet, headers, ignition and transmission. It runs great but I need it to pull a trailer 3 to 4 times a year and it has problems with grades. I thought about a rear end gear change but I am not sure what I have in it now and it would cost a bunch of money. I was close to buying a 96 F250 Diesel to pull the trailer but could not bring myself to buy a second truck that would sit most of the year and the money for the Ford could be spent on the Chevy.

First question is about tires. I foumd a good deal on two new Uniroyals at a swap meet for $100 so I put them on the rear. They are 265/75/R16 and have a 32" diameter. The front tires I just bought from Les Schwab are 245/75/R16 and have a 30" diameter. How much gear ratio would I gain by moving the front tires to the back? Could I get the gearing I need by going to an even smaller tire? What was the stock diameter tire that came with the truck?

What was the stock gear ratio on a 72 C20? What type of rear end was used. I know mine is not an Eaton because of the bolt pattern. I haven't been able to get under it to find a number on it and there are not tags.